1. Field of the Invention
The present invention relates to a novel spinal disc prosthesis and to a novel method of placing the prosthesis between adjacent vertebrae.
2. Description of the Prior Art
The vertebrae of the spine are each separated by a relatively soft disc which acts as a joint that allows the spine to flex, extend, bend laterally and rotate. Each disc includes a tough outer fibrous ring that binds the adjacent vertebrae together. The fibrous portion consists of overlapping multiple plies and are attached to the vertebrae in a manner that resists torsion whereby half of the angulated fibers making up the ring will tighten when the vertebrae rotate in either direction relative to each other. The inside of the disc has a high water content which aids in the load-bearing and cushioning properties of the disc. However, one or more discs in the spine can be displaced or damaged due to trauma or disease. A disc herniation occurs when the fibers are weakened or torn and the disc becomes permanently stressed, extended or extruded out of its normal confines. A herniated or slipped disc can compress a spinal nerve resulting in pain, loss of muscle control, or even paralysis. Also, the disc degeneration causes it to lose water and deflate. As a result, the height of the disc decreases causing it to buckle. As the buckling takes place, radial or annular tears may occur and contribute to persistent and disabling pain.
While a variety of procedures and disc prostheses have been developed and used heretofore, they often involve fixed rigid approaches and systems which do not restore normal function and require long and complex operations. Thus, there is a continuing need for improved disc prosthesis and a method of placing the prosthesis between vertebrae which is relatively simple and provides normal spine function without pain or disability.